Threshold measurements of theK-shell photoelectron satellites in Ne and Ar

The relative intensities of $K$-shell photoelectron satellites near their respective thresholds in Ne and Ar have been measured using synchrotron radiation. The Ne satellites were found to be 25-40% smaller than in the high-energy limit. The $2p\to 3s$ "conjugate shakeup" state of ${\mathrm{Ne}}^{+}$ was not observed, in contrast to predictions of many-body perturbation theory. The asymmetry parameter of the neon Auger group was found to be equal to zero at the $1s\to 3p$ resonance at 867 eV. This result may indicate that the $3p$ Rydberg electron is essentially decoupled from the core in the Auger decay process. In argon, a $K$-shell satellite was observed at 24.6(3) eV with 6% intensity relative to the main line, confirming a theoretical prediction by Dyall. Tentative evidence was obtained that this branching ratio increases with energy in the first 90 eV above threshold.